Vice-president Al Gore recently announced development of additional civilian signals to be provided by the satellite-based U.S. Global Positioning System (GPS). "The additional civilian signals will significantly improve navigation, positioning and timing services to millions of users worldwide--from backpackers and boaters to farmers and fishermen, from airline pilots to telecommunications provider, and from scientists to surveyors." Vice president Gore said. "GPS has become an engine of economic growth and efficiency as businesses and consumers are continually developing new and creative applications of the system." Indeed, applications of the GPS and other satellite-based positioning systems are evolving rapidly for commercial, public safety and national security purposes.
Public safety can benefit tremendously from application of global locating technology, if it can be done reliably, accurately and economically. Cell telephones are becoming ubiquitous in the U.S. and around the globe, giving users the ability to place a call, in particular an emergency call, from almost anywhere at any time. The difficulty is that it is difficult to determine the location of the mobile caller. For a fixed location or "landline" telephone, the technology to trace the call back to the telephone location is already in place. It is more difficult to locate a mobile caller, yet the need is exploding.
In Massachusetts alone, for example, there are reportedly 40,000 cellular 911 calls per month placed to the PSAP (Public Safety Access Point) in Framingham which is the point from which all cellular 911 calls are routed. According to the CTIA (Cellular Telecommunications Institute of America), in 1997 there were in excess of 18 million cellular 911 calls placed in the U.S. The problem of identifying the location of emergency 911 callers is exacerbated by the fact that the individual may not be conscious, may not speak the English language, may be too hysterical to give adequate information to the dispatchers, or more likely, does not know where he/she is. In a panic situation, most 911 callers have not a clue as to where they are.
The U.S. government has issued a challenge to the communications industry to fix the problem. The FCC presently requires that wireless carriers must locate a 911 call by cell sector. A more recent FCC Report and Order (see Docket Number 94-102; 96-264) requires that by 2001, covered carriers must have the capability to identify the latitude and longitude of a mobile unit making a 911 call within a radius of no more than 125 meters in 67% of all cases. Even greater accuracy will of course provide that much more benefit. For example, finding an injured person in a crowded urban center may be difficult--and delayed--where the location information is off by 100 meters. A "fix" within a few meters would be more useful.
Various methods to locate a caller or mobile unit, at least approximately, are known. In one commercial example, The Code Alarm Company of Madison Heights, Mich. offered a system in which a dedicated cellular phone was provided with a LORAN receiver and a separate LORAN antenna, with the result information being modemed to a central dispatch office in Wisconsin. This system was not well received because of costs that involved the payment for a dedicated cellular phone, the provision of a separate long whip LORAN antenna, and the fact that the calls were modemed to a central processing point from which services were to be dispatched. The utilization of a central processing office suffered from the problem of "no local knowledge" in which knowledge of local streets and terrain as well as local emergency services was lacking. That system is not a practical solution to meeting the FCC challenge.
Another known approach to determine the location of a cell phone user is triangulation. In a triangulation system, the cellular phone location was identified through a ranging technique and a transponder at the cell phone. This also requires special equipment at every cell tower. The estimated implementation cost of $500K per cell site, along with a deployment time of approximately two years per community, make triangulation relatively expensive and neither universal nor quickly implementable. It is also doubtful that triangulation would reliably provide sufficient accuracy of reported location.
Others have tried a time difference of arrival (TDOA) technique in which a data burst is received simultaneously at three cell sites. From the time difference of arrival of the data burst from the phone at each of the cell sites, the approximate location of the cellular telephone can be determined. The approximate cost of the one such system is $90K per cell site and again this approach can take at least two years per community to implement.
Another vendor called the Associated Group has implemented a TDOA system, dubbed their True Position System. This system is undergoing testing to ascertain location accuracy and cost of implementation. The estimated cost is reportedly $50K per cell site, but varies depending on the number of receivers (1-6) per cell site. As with any triangulation system, when the cell sites are in line, the lines between the towers and the cell phone come together at very shallow angles, reducing the accuracy with which position can be ascertained. Secondly, as with all triangulation systems , the coverage depends on towers being retrofitted with suitable antennas and infrastructure. These types of solutions would cost literally billions of dollars to implement throughout the U.S. Moreover, the ability of triangulation systems to locate any cell phone--requested by the user or not--has civil liberty implications.
Many believe that GPS rather than terrestrial triangulation holds the key to fast, accurate location of a user. In order for GPS receivers to operate, the 40 watt spread spectrum signals from the 26 satellites must be receivable by the GPS receiver on a line-of-sight basis. It has been found that cloud cover, trees, and other blocking artifacts other than buildings seem to have very little effect on the receipt of these signals which are 20 dB down by the time they reach the earth's surface. In general, as many as 8-12 GPS satellites are "visible" from any particular point on the earth, with the result that manufacturers such as Motorola, Garmin, Trimnble, Magellan, Rockwell, and others have provided 8-12 channel receivers for the receipt of the GPS signals. The satellites provide signals indicating their own position, e.g., ephemeris, and timing signals such that the GPS receivers can derive range to each of these satellites, from which the position is internally calculated by the GPS receiver. Various hand-held GPS receivers for consumers, and GPS receiver integrated circuits and boards for OEM use, are commercially available.
One early system utilizing GPS information to provide a PSAP with the location of a stricken vehicle was developed by Navsys Corporation of Boulder Colorado in which raw GPS data received by a GPS antenna mounted on the exterior of a car was transmitted to a central processing point provided by Navsys and the Department of Transportation for the State of Colorado to process the GPS information and to provide location to ISAP terminals within the State of Colorado. While the utilization of GPS-based location information proved adequate to locate the vehicles in question, the utilization of a central processing facility to process raw GPS data was found to be unwieldy, also limiting the portability of the system to other jurisdictions. U.S. Pat. No. 5,712,899 to Pace, II shows a mobile location reporting system that utilizes a cell phone and GPS data apparently much like the Navsys system; GPS data is transmitted to a base station, and there decoded to form latitude and longitude location information.
As reported by Tendler Cellular of Boston, Motorola developed the Encore system for the location of vehicles initially implementing the system in Lincoln automobiles. These systems were implemented through the utilization of a cellular phone coupled to the output of the Encore 8-channel GPS receiver, with the latitude and longitude location being modemed to Westinghouse in Irving, Texas for further dissemination to the closest PSAP to the vehicle. The system was initially configured to provide the PSAP with the Vehicle Identification Number and position information only, with this information provided to the relevant PSAP by calling a back line at the PSAP.
In an effort to ascertain back-up line telephone numbers, Westinghouse turned to the National Emergency Number Association or NENA for the provision of the telephone anumbers of the local PSAPS. Presently, the accuracy of such PSAP numbers is at the 80% level, as there are some 7,000 PSAPS in the United States. The utility of modeming information to a central processing dispatch center such that as maintained by Westinghouse is that the amount of infrastructure to be provided at the PSAP can be limited.
Tendler Cellular of Boston, Mass. describes an integrated, portable, unitary cellular phone incorporating a GPS receiver, a GPS antenna, a chipset for decoding the latitude and longitude derivable from the GPS receiver, and a synthesized voice indicating location. In other words, the Tendler system (cell phone) can call out to a PSAP, and then literally "tell" the operator, in synthesized voice (in English), the latitude and longitude location information. The system can also squawk the cell phone telephone number. The vendor claims that utilization of synthesized voice to announce the latitude and longitude of the E-911 caller results in a virtually infrastructureless system in which, through the provision of electronic maps on CDROM at a cost of no more than $300 per terminal, operators at the PSAPS can obtain a bulls-eye on the electronic chart by merely listening to the latitude and longitude, typing it in and receiving the bulls-eye. The Tendler system that uses synthesized voice to transmit location data is described in U.S. Pat. No. 5,555,286 assigned to Tendler Technologies, Inc.
Users and government agencies, however, have experienced difficulties with a synthesized voice system. The PSAP operator may not be skilled at recording and understanding "spoken" latitude and longitude data. The operator can make a mistake in transcribing the synthesized voice. Perhaps most important, synthesized voice data has very limited utility; it cannot be easily interfaced to other electronic systems to take automated actions based on that data.
Another public safety telephone system that includes cell phones is described in Grimes U.S. Pat. No. 5,388,147 assigned to AT&T. That 911 system provides for handling and routing both wired and wireless (cell) originated calls. Where the cell phone is connected to a GPS receiver, the GPS geo-coordinates are transmitted to the cellular switching system. Digital transmission is preferred, but an internal voice synthesizer can be actuated where digital data communication is not supported. This will often be the case, as digital data transmission systems, e.g. ISDN are available only in limited locations, and special decoders are needed as digital communication protocols are very dependent on hardware, firmware and software implementations and therefore are not universally available to support a universal public safety system.
In general, proposed location reporting telecommunication systems are too expensive to implement on a broad scale. Most of them require expensive equipment and or modifications to be made at every cell site, as well as downstream in the communications network. Systems that use the voice channel to transmit location data with voice synthesis, occupy the voice channel and thereby preclude actual voice communication (live person-to-person) over the same channel. In emergencies, a live voice connection can be critically important.
U.S. Pat. No. 5,043,736 describes a system for ascertaining the latitude and longitude of an individual or object at a remote location, and either using the location data locally (map display embedded in device) or transmitting the location data from the remote device (cellular network based) through a cellular telephone switching system (CTSS) to a base station for display. A pseudo-random code algorithm is used for correlating a position fix from the Global Positioning System (GPS) receiver, and the position fix is stored RAM, for transmission via a "special cellular modem" to a base station. Accordingly, specialized equipment is needed both in the remote device and a special "base station".
The need remains for improvements in location transmission methods and apparatus, for public safety and for other applications. Improvements are needed to improve location accuracy; to lower costs; to provide for continuously updated location information; to provide for correction of geo-position information; to implement improved, automatic routing capabilities, etc. These and other improvements are provided by the present invention in its various aspects.